Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
How to shutdown a frozen Linux System?
Answer:
Similar to this post, but this time you are going to shutdown a frozen Linux system.
The last letter O tell the system to shutdown. Replace by the letter R if you want reboot instead.
Sum of every lines' value in a file
Answer:
Assume you have a file num.txt
1
2
3
4
5
How do you calculate the sum of every lines' value in a file?
Use Perl!
# perl -lne '$x += $_; END { print $x; }' < num.txt
15
Benchmark Perl subroutines
Answer:
The Benchmark module provide a very easy way to compare (cmpthese) the performance of Perl's subroutines.
E.g. The following codes compare the performance of MD5 and SHA1 hashing methods.
#!/usr/local/bin/perl
use strict;
use Benchmark qw(cmpthese);
use Digest::MD5 qw(md5_hex);
use Digest::SHA1 qw(sha1_hex);
my $str = '83b0c3d63e8a11eb6e40077030b59e95bfe31ffa';
my $s;
cmpthese( 1_000_000, {
'md5' => sub{ $s = md5_hex($str) },
'sha1' => sub{ $s = sha1_hex($str) }
});
It will output
# perl compare_md5_sha1.pl
Rate sha1 md5
sha1 934579/s -- -39%
md5 1538462/s 65% --
Obviously, MD5 is faster than SHA1.
Turn on expire headers in Apache
Answer:
By turning on the expire headers, browser will cache the files serving from Apache more aggressively, so as to reduce traffic loading to the Apache web server.
Steps:
Add the following lines to the Apache configuration (httpd.conf)
<IfModule mod_expires.c>
ExpiresActive On
# Cache all files for 2 weeks after access (A).
ExpiresDefault A1209600
# Do not cache dynamically generated pages.
ExpiresByType text/html A1
</IfModule>
Restart Apache to take effect
# apachectl -k graceful
Assume the module mod_expires is enabled
Convert HTML to image
Answer:
Firstly, you need to install html2ps
# sudo apt-get install html2ps
Then install the ImageMagick
# sudo apt-get install imagemagick
Finally run the command:
# convert -density 72 input.html output.png
